Diagnóstico do estado nitrogenado e manejo da água no cultivo do arroz irrigado tropical
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2021-02-23
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Universidade Federal de Goiás
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In Brazil rice production is concentrated in the South under the irrigated system. For reasons of food security, there is a need to distribute production in the country. Significant gains in grain yield have been associated with applications of high amounts of nitrogen. However, when assessing the efficiency of the use of nitrogen (EUN) [kg of grain produced / kg of applied N], utilization of less than 40% has been observed. Thus, strategic nitrogen management is crucial for high-efficiency agricultural production and sustainable agriculture. In addition to the need to increase the EUN, there is a growing interest in reducing the volume of water used in irrigated rice farming with the application of continuous water depth throughout the cycle. With the reduction in the volume of water applied with this management, in addition to the reduction in the cost of production, there is an increase in water use efficiency and EUN. Thus, intelligent and premeditated interventions in relation to natural resources must be carried out in order to optimize the management of N and to reduce water use, without reducing productivity. The objective of this study was to determine potential vegetation indices for diagnosing the nitrogen status of the crop and to evaluate impacts of water depth management on morphophysiological characteristics and grain yield of contrasting irrigated rice cultivars. The state of N in the plants was evaluated from vegetation indexes obtained with the canopy reflectance to the radiation offered by low altitude optical sensor. From the combination of three spectral bands of reflectance, 22 vegetation indices (IV) were calculated and evaluated for their efficiency in estimating the state of N during periods of growth of irrigated rice. The results of this study indicated that the selected IVs considerably underestimate the dry leaf biomass and did not efficiently estimate the nitrogen indicators in the crop, such as the concentration and accumulation of leaf nitrogen, in the growing season. Greater variations in these indicators can be explained by the IV in subsequent periods. The IV selected in the calibration process proved to be highly promising for explaining the variation of dry leaf biomass and the leaf area index in the reproductive and grain filling periods. However, modest IV performances were obtained to estimate leaf nitrogen concentration in the reproductive period. The vegetation index adjusted to the modified red edge soil (M_RESAVI) and the red edge index by normalized difference (NDRE) showed high performance in estimating the nitrogen nutrition index (INN) in all growth periods, as well as in the cycle whole. These results show the importance of using active sensors with more than two fixed bands, especially with the addition of the red border band, to better estimate the nitrogen status of the culture. The effect of alternative irrigation managements on phenological development, gas exchange, biomass accumulation and productivity of tropical irrigated rice was also studied. Two experiments were conducted in Goianira-GO from 2016 to 2018 to evaluate the effect of irrigation managements: intermittent flooding with aeration (IIA), intermittent flooding throughout the cycle (IIC) and intermittent flooding until flowering (IIF) in relation to management continuous flooding throughout the cycle (ICC). In these experiments, four rice cultivars were studied: BRS A702 CL, BRS Catiana, BRS Pampeira and IRGA 424. The data on phenology, gas exchange, growth dynamics and productivity were subjected to joint analysis to produce general inferences in cultivation. Irrigation management did not affect the vegetative development of the crop. The intermittent flooding with aeration prolonged the flowering time for cultivar BRS A702 CL. It was found that it is possible to decrease the water supply with the maintenance of saturated soil or the use of intermittent flooding until flowering, or even, throughout the cycle, without compromising transpiration. There was no direct relationship between the accumulation of biomass due to differences in the photosynthetic rate between cultivars and irrigation management. The accumulation of dry biomass was reduced by the occurrence of smaller accumulations of radiation and degree-days in the reproductive and grain filling phases. Grain productivity and harvest index were similar between the irrigation management investigated. The findings of this study allow us to infer that the management of the state of N in irrigated rice can be done from the INN estimated by the M_RESAVI and NDRE indices and that strategies that rationalize water use such as: intermittent flooding with aeration (IIA) and intermittent flooding the whole cycle (IIC) can be adopted in the cultivation of tropical irrigated rice without damage to grain productivity.
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SANTOS, M. P. Diagnóstico do estado nitrogenado e manejo da água no cultivo do arroz irrigado tropical. 2021. 109 f. Tese (Doutorado em Agronomia) - Universidade Federal de Goiás, Goiânia, 2021.